Article - The New IHO S-102 Standard - Caris

The New IHO S-102
Standard
Charting a New Frontier for Bathymetry
Soundings and contours are the only official way data producers can push bathymetric information to the wide
hydrographic community. The introduction of the S-102 standard for bathymetry will enable many possibilities within the
community of bathymetry users. Liaising with the International Hydrographic Organization’s (IHO) TSMAD working group,
the Canadian Hydrographic Service (CHS) and the US Naval Oceanographic Office (NAVO) led the development and
practical testing of this revolutionary standard, officially called the Bathymetric Surface Product Specification S 102. In
partnership with IIC Technologies, GeoNet Technologies, and CARIS, CHS created one of the first prototypes of S 102
datasets, using the CARIS Bathy DataBASE software suite. A portfolio of 86 high-definition bathymetric charts was
subsequently produced within a few weeks, successfully validating a specification that will potentially change the
manipulation of bathymetric data we’ve known for years.
Marc Journault
Canadian
Hydrographic
Service
Louis Maltais
Canadian
Hydrographic
Service
Ed Kuwalek
IIC Technologies,
Canada
In shallow-water, ships navigation
and manoeuvring commands precautions
and decisions made with
the best information available and
usable in a secure manner. In these
circumstances, the most recent
details of the bottom shape are usually
considered essential. A three
dimensional ‘picture’ of the bottom
would meet this requirement,
and this is exactly what is meant by
High-Definition Gridded Bathymetry
(HDGB).
The grid bathymetry can be
described as a Navigation Surface
(developed by Shep Smith) or a Digital
Terrain Model (DTM) of the
seafloor in the form of regular rectangular
meshes. By its nature, the
resolution or the density of bathymetric
data collected usually varies
according to the depth range, and it
would be arguable to fix a quantitative
value to the term high definition
for bathymetry. In spite of this, the
concept of HDGB used in this article
is simply defined as a much higher
resolution than what is available on
the charts. For the source bathymetry
coming from a multi-beam system
the resolution can be similar to
the insonified footprint. For digitised
legacy data this can be the equivalent
of a field sheet density.
The existing tools to process and
manage bathymetric data generate
and combine grid datasets that are
used for chart compilation and contour
generation. Such grid datasets
of bathymetry can also be a product
by itself, created for different usage
like hydrodynamic modelling, spatial
data analysis with GIS, coastal management
with land DTM, or marine
navigation.
To develop a HDGB product for
navigation CHS adopted a collaborative
approach where navigators
and software manufacturers were
informed of the intentions and consulted
for specifications of a future
product. For the consultation, prototype
datasets were produced and
made available in a simple format
for experimentation and trials. The
work of the IHO Transfer Standard
Maintenance and Application Development
working group (TSMAD)
on the new Geospatial Standard
for Hydrographic Data (S-100) was
promising and CHS decided to use
it. S-100 is a framework standard for
the registration, maintenance and
capture of hydrographic geospatial
data and product specifications. It is
based on the international ISO 19000
series of geographic standards, and
it is flexible. CHS and NAVO worked
together to draft and propose a product
specification for grid bathymetry
based on previous work done by the
Open Navigation Surface group. The
standard is named Bathymetric Surface
Product Specification and identified
as S-102.
At the 3 rd HSSC meeting in November
2011, the IHO TSMAD invited
the Hydrographic Services and
Standards Committee (HSSC) to
approve the final draft of S-102 and
instruct the IHB to submit it to
Member States for their endorsement.
Subsequently, the IHO circular
Hydro international | may 2012 | 21

Figure 1: Example
of a level 2
(coastal) tiling
scheme for the
St.Lawrence River.
letter 10/2012 requested the Member
States to review and consider the
draft edition of S-102 which is available
on the IHO website.
To partition HDGB coverage, to allow
unambiguous dataset exchange and
to facilitate the updates, CHS intends
to implement a systematic tiling
scheme with three levels of resolution.
Each tile is comprised of 1000 by
1000 grid cells, the level 1 (harbour)
is 0.02º x 0.02º, the level 2 (coastal) is
0.1º x 0.1º, and the level 3 (overview) is
1º x 1º. For the low and mid latitudes,
the orientation of the tiles fit the
version of the IHO S-102 product
specification. Developing a uniform,
high-definition bathymetric surface
for the St. Lawrence River between
ports of Quebec and Montreal was the
key goal for the project. In addition, as
this was the first attempt to produce
a large number of datasets based on
this new product specification, the
project provided an ideal opportunity
to validate the feasibility of S-102 production
in practice.
The main requirements for the portfolio
included creating seamless
data coverage with a final surface
S-100 framework standard
represents a step foreword for
electronic navigation products
and services
meridians and parallels with an origin
based on a round number in latitude
and longitude. Figure 1 shows an
example of the tiling scheme.
Production of Datasets for Trials
In January 2011, CHS contracted
IIC Technologies and GeoNet Technologies
to produce a portfolio of
86 HDGB datasets based on a draft
grid resolution of 0.0001º (approximately
8 metres) divided into 0.1º x
0.1º tiled datasets. The final bathymetric
surface needed to be created
by integrating a variety of source
datasets available for the area, ranging
from sparse sounding sets to
much higher resolution grid data
for channels, while also using ENCderived
high-water lines along with
the corresponding drying spot values.
The intention behind using all
available source data was to integrate
all information in a complete dataset,
capable of significantly enhancing
the information already available
on the ENC cells. Similarly the project
required the deliverables to be provided
in multiple formats including
CSAR (CARIS Spatial Archive), BAG
and 32-bit GeoTiff files to cater to a
variety of potential end-users.
The production processes consisted
of four main stages: source data
assessment and preparation, point
data processing, surface data integration
and conflict resolution, and
final product surface extraction
and export. During the first stage all
source data was assessed and prepared
for production. CARIS S-57
Composer and BASE Editor were
used to create all auxiliary components,
such as the tiling scheme, coverage,
and breakline vector layers. The
same tools were also used to cut all
data sources into individual data tiles
to facilitate their efficient processing.
During stage two the XYZ point
data was loaded into BASE Editor
and used to build a TIN model which
was enhanced by the addition of the
high-water-based breakline vector
layer. Subsequently, a high-resolution
bathymetric surface was interpolated
from the TIN models for each dataset.
During stage three the additional
22 | may 2012 | Hydro international

which will be identified as mandatory,
conditional or optional, will be
selected from these ISO 19115 metadata
packages.
Figure 2: S-102 Production Process.
high-definition surface data available
for channels was merged with
the product surface data created in
stage two. This was achieved by using
rule-based conflict resolution tool
available in BASE Editor. In the final
stage the coverage polygon was used
to extract the final product surface,
effectively facilitating a complete
river bank to river bank data coverage.
Thereafter BASE Editor was used
to export CSAR and BAG deliverables
and CARIS Easy View was used
to export 32-bit GeoTiff rasters. Figure
2 illustrates the key stages of the
data production process used during
the project.
All project goals were successfully
achieved and the required portfolio
of 86 HDGB datasets was efficiently
produced, confirming the feasibility
of HDGB data production using the
currently available CARIS production
tools.
Generation of S-102
Bathymetry Grids
As described above, the interpolated
grids from the point data are combined
with the high-definition grids
from the ship channel to produce the
final grids for each cell, in the CSAR
format, which are then exported to
the desired carrier format of the grid.
The draft S-102 standard follows the
principle of separating the ‘carrier’
from the ‘content’ which means that
the encoding of the grids will be flexible.
Following that principle, the
CARIS software tools provide choices
for export formats. At the time of this
S-102 prototype work, the choices
were:
• 32bit Floating Point GeoTIFF format.
This option for a carrier format
is available from the GDAL
open source library ( 1). The
32bit floating point option is used
so that the depth values can be
encoded without loss of precision.
• BAG format. At the time, the
CARIS Bathy DataBASE (BDB) v3.1
supported BAG v1.3. The support
for BAG format is possible through
the API provided by the Open Navigation
Surface Working Group (
2) of which CARIS is a participant.
Since then, BDB has been updated
to support BAG v1.4. CARIS is currently
working with the ONSWG on
BAG v1.5, which will be supported
when finalised and released.
Metadata
Adjusting this production line to
match the coming S-102 standard is
going to require the creation of metadata
that is compliant with the S-102
profile. The details of the S 102 metadata
profile are still being developed
but many aspects of the content are
already known. Fortunately, this area
has received significant attention
over the past two years at CARIS with
the creation of the metadata profile
for the CSAR format that is compliant
with the ISO 19115 / 19115-2 standards
and using XML encoding from
ISO 19139. Drafts of the S-102 standard
indicate that its metadata profile
will share many of the same elements
that are already being populated in
exported CSAR metadata XML files.
The drafts of S-102 metadata profile
indicate that most of the core metadata
elements in the profile, each of
Evolution of CARIS BDB and
S-102 Software Tools
In the period since these prototype
S-102 gridded products were produced,
the software tools have evolved
which could improve the workflow
even further. For example, the Warp
function, which has been available
since BDB 3.2, can transform a gridded
surface to a new coordinate system
and/or re-sample the surface
onto a new grid resolution. This could
save steps in turning what started out
as projected bathymetry in grid resolutions
of metres on the ground, into
unprojected grids at the appropriate
decimal degree resolutions with one
function.
The next step in the evolution of software
tools for S-102 production will
be the creation of a new Export to
S-102 procedure that addresses the
following all in one function:
• Take a CSAR grid as input which
has been prepared with the correct
coordinate system and grid
resolution.
• Select an option for the output ‘carrier’
format of the gridded bathymetry.
(e.g. GeoTIFF, BAG, and others
as required)
• Optionally apply a tiling scheme
which will cut the input grid into
the desired tiles of specified width/
height in decimal degrees.
• Apply a defined naming convention
to the output tiled files.
• Generate an accompanying XML
metadata. This metadata could
then be used by data producers to
populate a metadata catalogue web
service
S-102 Gridded Bathymetry
on the Web
The CARIS web mapping solution,
Spatial Fusion Enterprise (SFE), supports
the discovery and dissemination
of high-definition bathymetry
through the Internet using OGC,
Open Geospatial Consortium ( 3),
standard formats. S-102 bathymetric
datasets residing in the CARIS BDB
database as CSAR grids are requested
by SFE through a specialised bathymetry
web service. The CSAR format
was designed with the optimisation
Hydro international | may 2012 | 23

Figure 3: Filtered ENC and S-102 in background.
required for web distribution of this
type of data in mind. OGC requests
are made from any OGC capable client.
The SFE Server handles the OGC
request and returns the relevant information
residing in the bathymetry
database. SFE currently supports the
OGC WMS, WMTS or WCS services
for bathymetry data: it is the WCS
(Web Coverage Service) that provides
download capabilities for the grids
including options for the format to be
received from the download. Efficient
browsing and simple query capabilities
are increasingly being provided
through the use of WMTS (Web Map
Tile Service) which is a variant on
the traditional WMS (Web Map Service)
protocol which chunks data into
image tiles. These tiles are cached on
initial draw meaning that the next
time an image request is made the tile
is drawn from cache rather than by
going back to the database.
Use of S-102 for navigation
With S-102 it will be easy for hydrographers
to provide navigators with
HDGB datasets very rapidly to enrich
and update the information of their
ENCs. Partitioned into standardised
regular geographic cells, the provision
of updates becomes easy by just supplying
an entire new cell dataset with
the new bathymetry to the users who
then just supersedes the tile.
A possible way to use HDGB for navigation
is to put the S-102 data in the
background with an overlap of S-101
without the display of S-101 soundings,
depth areas and contours.
Figure 3 shows such usage.
But electronic chart systems manufacturers
can do more than just displaying
it. The HDGB can be used: to
generate safety contour on the fly; to
compute the available water column
by the addition of water level (tidal
data) on top of the bathymetry; to calculate
a dynamic under keel clearance;
etc.
The exploitation of HDGB in an innovative
way is left to the users and the
software industry. The CHS and its
partners wish to involve them at an
early stage of design to consider feedback
from the users’ communities.
Conclusion
The IHO S-100 framework standard
represents a step foreword for
electronic navigation products and
services. This flexible standard is a
building block to rethink the way
hydrographic organisations (HO) can
deliver their official data and services.
This S-102 experiment clearly showed
how modern tools and standards will
enable quick delivery of rich bathymetric
information. It’s time to take
a step ahead and test these datasets
with users. This year the focus will be
on getting the ECS and ECDIS manufacturers
involved in exploring the
possibilities of S-102.
The Authors
Marc Journault has been working for
the Canadian Hydrographic Service for 28
years. He is manager of the Quebec region’s
Marine Geomatics Division, responsible for
technological support and development in
the fields of hydrographic surveys, nautical
publications and marine services.
Louis Maltais has been working for the
Canadian Hydrographic Service (CHS) for 13
years. He is involved in numerous R&D projects,
implementing solutions to improve productivity,
efficiencies and to better meet the clients’
needs.
Ed Kuwalek is the director of R&D at IIC
Technologies in North Vancouver, Canada. Mr.
Kuwalek has 18 years of experience in the field
of nautical charting, electronic-chart production
systems and spatial data conversions. He has
been involved in the technical leadership of
many industry-leading projects and is an active
participant in the IHO Transfer Standard and
Maintenance Working Group.
1. www.gdal.org
2. www.opennavsurf.org
3. www.opengeospatial.org
Hydro international | may 2012 | 25